In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there have been, and continue to be, efforts toward scaling down device dimensions (e.g., at sub-micron levels) on semiconductor wafers. In order to accomplish such high device packing densities, smaller and smaller features sizes are required. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, and the surface geometry, such as corners and edges, of various features. The dimensions of and between such small features can be referred to as critical dimensions (CDs). Reducing CDs, and reproducing more accurate CDs facilitates achieving such higher device densities. Conventional lithographic processes employed to produce such features depend, at least in part, on the quality of reticles employed in fabricating the integrated circuits. Thus, improvements in reticle fabrication quality are desired.
Reticle manufacture can involve phases including, but not limited to depositing a photoresist on a reticle, exposing a pattern into the photoresist, post exposure baking, developing the pattern exposed into the photoresist, etching the photoresist and/or mask and stripping the resist. Conventionally, metrology associated with each phase has been handled independently, which results in missed opportunities for improved process control.
By way of illustration, a photoresist application process employed in manufacturing a reticle may rely on preprogrammed times, temperatures, formulae, etc., to deposit photoresist on a reticle. The photoresist application process may be monitored to facilitate determining when a desired application has occurred, but such information gathered during this phase is typically employed only during this phase. Thus, opportunities to improve downstream processes are lost.
By way of further illustration, a subsequent reticle manufacture phase, (e.g., post exposure bake, development) may similarly apply pre-programmed times, temperatures, formulae etc. that are based on historical performance, where the times, temperatures, formulae and the like may have to account for deviations in previous reticle fabrication steps.
By way of still further illustration, conventional etch processes have either lacked control systems, requiring pre-calculated etching steps, or have had indirect control, which is based on indirect information (e.g., amount of gas generated by plasma gas discharge etching). Such pre-determined calculations and/or indirect feedback control do not provide adequate monitoring and thus do not facilitate precise control over the etch process. Furthermore, such pre-determined calculations and/or indirect feedback control do not account for variations produced in previous reticle fabrication phases. Monitoring tools employed in conjunction with feed back control are known in the art and provide improvements over time based control. But such feed back systems suffer from operating in isolation.
The process of manufacturing semiconductors (e.g., integrated circuits, ICs, chips) employing reticles typically consists of more than a hundred steps, during which hundreds of copies of an integrated circuit may be formed on a single wafer. Generally, the process involves creating several patterned layers on and into the substrate that ultimately forms the complete integrated circuit. The patterned layers are created, in part, by the light that passes through the reticles. Thus, processing the positive or negative of the pattern into the reticle is important in fabricating the chips.
Unfortunately, commonly used fabrication systems check reticle CDs near or at the end of fabrication, or at pre-scheduled time intervals. These types of end-point and interval detection methods can be problematic for several reasons. For example, at late stages in the fabrication process, the presence of at least one mal-formed portion may render the reticle unusable, forcing it to be discarded. In addition, post-fabrication detection/quality control data does not provide a user with real-time information related to the reticle being fabricated. Post-fabrication data may only allow an estimation or a projection as to what adjustments are needed to correct the fabrication errors and/or flaws. Such estimations and/or projections concerning necessary adjustments may lead to continued or recurring fabrication errors. Moreover, such a lengthy adjustment process may cause subsequently fabricated reticles to be wasted in the hopes of mitigating etch process errors.
Visual inspection methods have been important in both production and development of reticles. For example, visually inspecting developed photoresist patterns from a dose-focus matrix is well-known in the art. While visual inspection techniques may be simple to implement, they are difficult to automate, and furthermore, have typically operated in isolation from other fabrication phases. Further, visual techniques employing scanning electron microscopes (SEM) and atomic force microscopes (AFM) can be expensive, time-consuming and/or destructive.